Note: Javascript is disabled or is not supported by your browser. For this reason, some items on this page will be unavailable. For more information about this message, please visit this page: About CDC.gov.

Preparing a Dietary Analytic Dataset

Dietary data are among the most complex of all
the data in NHANES. For this reason, preparing a dataset for
dietary analysis is an especially critical set of steps and often
may be more time-consuming than the analysis itself.

Analysts working with NHANES dietary data
frequently want to be able to answer the following types of questions:

What is the mean intake of a given food?

What is the mean intake of a given nutrient from all foods
and beverages?

What is the mean intake of a given nutrient from
supplements?

Which foods are the major sources of a given nutrient?

What is the distribution of intake of a given food or
nutrient across a selected population?

How does dietary intake relate to some health parameter?

To conduct these analyses, you will first need to
know how to successfully complete the tasks described in the following
modules of the Preparing an Analytic Dataset course:

As you
work your way through these modules, and eventually prepare your own
analytic dataset, it is useful to keep in mind three issues that add to
the challenge of dietary data analysis—the unit of analysis,
variable definitions, and the inferred population. All of these
issues require that you think very specifically about your research
question.

IMPORTANT NOTE

This tutorial uses the SAS convention of using the
term "variable" to refer to a field in a dataset.

One of the reasons that dietary data are so complex is
because the unit of analysis may vary. The basic unit of analysis in
NHANES is the individual participant, identified by the variable SEQN.
However, because of the way the dietary data are structured—with
individuals having multiple food and dietary supplement records, which
in turn have their own accompanying sets of variables—the unit of
analysis for some types of analyses is at the level of the food or
supplement, rather than the individual.

Dietary data also are challenging to work with because many analyses
require the creation of new variables from variables that are found
in the survey data files. For example, if you are interested in
finding the answer to the question “What is the mean intake of milk
among survey participants?,” the way you define “milk” (e.g., all
types of fluid milk consumed as a beverage, or milk also consumed as
an ingredient in other foods, or servings of milk as defined by the
guidance in MyPyramid) may require you to create several new
variables based on your analytic needs.

IMPORTANT NOTE

The modules in this course require some basic knowledge of statistics as well as statistical software (e.g. SAS and SUDAAN) and programming.

Before you get started

If
you have questions about this tutorial as a whole:

Read the
Introduction
to find answers to frequently asked questions about NHANES dietary data
and this tutorial.

Browse through the
Logistics
section to learn about the web layouts and templates used in the
tutorial and find out the basic knowledge and skills you’ll need to use
the tutorial.

Go to
Technical & Software Requirements
for information about what’s required to view the tutorials correctly
and run the sample programs properly. This section also is the place to go
if you need help with technical problems.

Sample Code

Abbreviated SAS and SUDAAN code is presented throughout the tutorial
for the sole purpose of demonstrating and explaining specific steps in
an analysis. The abbreviated code does not comprise a complete SAS or
SUDAAN program that can be readily submitted for a computer run. If you
need the complete SAS or SUDAAN program, please consult the Additional
Resources section of this tutorial.

Before you get started

Read the
Introduction
to find answers to frequently asked questions about NHANES dietary data
and this tutorial.

Browse through the
Logistics
section to learn about the web layouts and templates used in the
tutorial and find out the basic knowledge and skills you’ll need to use
the tutorial.

Go to
Technical & Software Requirements
for information about what’s required to view the tutorials correctly
and run the sample programs properly. This section also is the place to go
if you need help with technical problems.

Course Registration and Quizzes

Go to the CDC/ATSDR Training and Continuing Education Online at
http://www.cdc.gov/TCEOnline. If you have not registered as a
participant, click on New Participant to create a user ID and
password; otherwise click on Participant Login and login.

Once logged in to the CDC/ATSDR Training and Continuing Education
Online website, you will be on the
Participant Services page. Click on Search and Register. Enter
the course number
WB1352 or
a keyword under Keyword Search. Click on View.

To get Continuing Education credit, click on the course entitled
“NHANES Dietary Tutorial – Preparing an
Analytic Dataset.” Select the
type of CE credit you would like to receive and then click the Submit
button. You will be prompted to answer three questions about
yourself. After answering the questions, click Submit. A
message will appear confirming your registration. After you complete the
modules of the course, you will need to complete a final exam and course
evaluation to receive Continuing Education credit. A record of your
course completion will be stored in the Transcript and Certificate
section of the training website.

If you have any questions or problems with the
CDC/ATSDR Training and Continuing Education Online website please
contact: